Answer
$1$
Work Step by Step
Step 1. Rewrite the equation as $\sqrt x=\sqrt {x+3}-1$
Step 2. Take square on both sides to get $x=x+3-2\sqrt {x+3}+1\longrightarrow \sqrt {x+3}=2$
Step 3. Take square on both sides to get $x+3=2^2$, thus $x=1$
Step 4. Check the answer with the original equation and it fits.